The present invention relates to a lens system having five lens components, an aperture ratio of 1:2.8 and a viewing angle of about 24.degree. in which a stop diaphragm is disposed at a rear part of the composite lens system and aberrations are well compensated for.
In general, in many cases, a photographic lens is designed so that a stop diaphragm may be disposed in an air space between selected ones of the lessons. In a specific case, it is also required to provide a stop diaphragm outside of the lens system. In some cameras, it is structurally more convenient to position a shutter and a stop diaphragm behind the lens system. A lens having a rear stop diaphragm may also be a requirement. However, in such a lens, there is an undesirable limitation to the aberration compensation in comparison with other lenses. In addition, it is difficult in such a lens to maintain good optical properties not only in the open state of the stop diaphragm but in each stop-down state. This remains a problem to be solved in a lens having the rear stop diaphragm since there is a requirement that a sufficient amount of peripheral or marginal light be obtained even if the stop value is set to a minimal aperture value. Accordingly, the diameters of the rear lenses must be necessarily broadened although at the same time it becomes difficult to compensate for the aberrations near the outermost portions thereof.
In order to solve the above-noted problems in accordance with one prior art technique, the diameters of the front lenses were reduced. For this, it is necessary to shorten the overall length of the lens system. As a result, the power of each lens must be excessively high so that it is difficult to compensate for various aberrations, particularly, spherical aberration.